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4.  Ammonia .-—This is estimated by distilling with excess of caustic

soda (see Fertilisers).

5.  Determination of the Boric Acid.-—This is readily effected by
Jorgensen's modification of Honig and Spitz's volumetric method :   10
grams of the acid are dissolved in 500 c.c. of recently boiled water and to
50 c.c. of the solution (i gram of substance) are added 50 c.c. of pure glycerine
(previously neutralised with caustic soda, if the is acid) and a few
drops of phenolphthalein.   The liquid is then titrated with N/a-sodhun or
barium hydroxide  (absolutely free from carbonates) until a red coloration
is just reached;  a further 10 c.c. of the glycerine are added and, if the
colour disappears, the. titration is continued, this process being repeated
until addition of glycerine no longer destroys the red colour.    This is the
case when i mol. of HaB03 is combined with i mol. of NaOH ;   i c.c. of
N/2-alkali = 0-031 gram of H3BOa.

Commercial crude boric acid contains 80-95% HaBO., and the refuted product
not less than 99%.


CO, - 44

This is sold in the liquefied condition, compressed in steel cylinders of
various capacities. It may contain air, carbonic oxide, mineral acids,
empyreumatic substances and various mechanical impurities (especially
lubricating oils), which collect at the bottom of the, vessel as a, thick, brown
liquid of repulsive, odour. Analysis comprises the. following:

1.   Gaseous Impurities ."--The gas is introduced into a graduated
cylinder over mercury l and there left in contact with a, few c.c,. of boiled,
concentrated caustic soda solution ; the residual unabsorbed gas represents
the gaseous impurities of the carbonic acid.   According 1o Werder," the
carbonic acid may be passed.through an Orsat apparatus with three absorp-
tion bulbs, the first containing potassium hydroxide solution to absorb the
carbon dioxide, the second potassium pyrogallate, solution to absorb the
oxygen and the third aminoniacal cuprous chloride, solution for the, carbon


2.  Empyreumatic  Substances.--A  current  of  the.  gas  is  passed

through concentrated sulphuric acid ; if the gas is impure, the acid becomes


3.  Sulphurous and Nitrous Acids.-   If either of these is present,

passage of the gas through potassium permanganate solution gradually
decolorises the latter.

4.  Hydrochloric Acid.' -When this is present, passage of the gas
through a dilute silver nitrate solution acidified with nitric acid renders
the liquid turbid.

As a rule the acid of commerce is moderately pure and eon tain's only small
proportions of air (up to 6%), and rarely carbon monoxide (up to 4%). A good
carbonic acid should contain at least 98% by volume of (H.)a and not more than
0-5% of CO, and should be free from mineral acids and empyreumutk*. substances.

1 Instead of a cylinder over mercury, a Winkler burette, or any other form of gus-
measuring apparatus may be used.
z Chem, Zeit., 1906, p. 1021.ecessary, the estimation of the